The motherboards of the present computer systems mostly adopt ATX (Advanced Technology Extended) architecture. Compared with the traditional AT (Advanced Technology) architecture, the most significant feature of ATX architecture is adding a regular power supply of 5 VSB and makes 3.3V the standard supply voltage. To provide suitable power supply to the ATX motherboard the power supply must have capability to provide corresponding power output, including output voltages at 3.3V, 5V and 12V.
The conventional power supply conforming to the ATX architecture generally has an AC/DC transformer to generate DC power of different voltages to supply the ATX motherboard. However, energy conversion efficiency to generate the DC power through AC/DC transformation still leaves a lots to be desired, hence is not a satisfactory approach especially at present when energy saving is a big concern in the industry and public opinion. Moreover, output DC power is not stable in the aforesaid approach and operation of the motherboard could be affected. To address the concerns mentioned above, a technology adopted a Voltage Regulator Module (VRM) has been developed. Adopted such a technique, the AC/DC transformer of the power supply outputs only DC power of 12V, and a VRM circuit is added at the rear end of the transformer to allow the DC power of 12V to be transformed through a DC/DC approach to become DC power of 5V or 3.3V. The DC/DC transformation has improved energy transformation efficiency over the AC/DC transformation. Thus energy resource can be better utilized and energy saving effect can be achieved. In addition, DC/DC transformation also provides more stable DC power at low voltages, therefore can enhance operation reliability of the motherboard.
While the power supply adopted the VRM circuit has improved energy transformation efficiency, there is a time difference in output of DC power of 12V and 5V/3.3V. Referring to FIG. 4, when the power supply is started, the DC power of 12V can be output after time t1 is elapsed, but the DC power of 5V/3.3V can be supplied only after time t2 has elapsed. Namely the DC power of 12V and 5V/3.3V are supplied at different times of t1 and t2. The difference of t1−t2 also is called a time interval. In the general machine start condition, in order to ensure that the power supply providing an effective supply voltage, the ATX motherboard detects whether the power provided by the power supply is normal. As the conventional power supply adopted the VRM circuit forms the time interval t1−t2 on DC power of different voltages, the ATX motherboard could make misjudgment during detection and result in start failure of the computer system.